bpo-40503: PEP 615: Tests and implementation for zoneinfo (GH-19909)

This is the initial implementation of PEP 615, the zoneinfo module,
ported from the standalone reference implementation (see
https://www.python.org/dev/peps/pep-0615/#reference-implementation for a
link, which has a more detailed commit history).

This includes (hopefully) all functional elements described in the PEP,
but documentation is found in a separate PR. This includes:

1. A pure python implementation of the ZoneInfo class
2. A C accelerated implementation of the ZoneInfo class
3. Tests with 100% branch coverage for the Python code (though C code
   coverage is less than 100%).
4. A compile-time configuration option on Linux (though not on Windows)

Differences from the reference implementation:

- The module is arranged slightly differently: the accelerated module is
  `_zoneinfo` rather than `zoneinfo._czoneinfo`, which also necessitates
  some changes in the test support function. (Suggested by Victor
  Stinner and Steve Dower.)
- The tests are arranged slightly differently and do not include the
  property tests. The tests live at test/test_zoneinfo/test_zoneinfo.py
  rather than test/test_zoneinfo.py or test/test_zoneinfo/__init__.py
  because we may do some refactoring in the future that would likely
  require this separation anyway; we may:
        - include the property tests
        - automatically run all the tests against both pure Python and C,
          rather than manually constructing C and Python test classes (similar
          to the way this works with test_datetime.py, which generates C
          and Python test cases from datetimetester.py).
- This includes a compile-time configuration option on Linux (though not
  on Windows); added with much help from Thomas Wouters.
- Integration into the CPython build system is obviously different from
  building a standalone zoneinfo module wheel.
- This includes configuration to install the tzdata package as part of
  CI, though only on the coverage jobs. Introducing a PyPI dependency as
  part of the CI build was controversial, and this is seen as less of a
  major change, since the coverage jobs already depend on pip and PyPI.

Additional changes that were introduced as part of this PR, most / all of
which were backported to the reference implementation:

- Fixed reference and memory leaks

    With much debugging help from Pablo Galindo

- Added smoke tests ensuring that the C and Python modules are built

    The import machinery can be somewhat fragile, and the "seamlessly falls
    back to pure Python" nature of this module makes it so that a problem
    building the C extension or a failure to import the pure Python version
    might easily go unnoticed.

- Adjustments to zoneinfo.__dir__

    Suggested by Petr Viktorin.

- Slight refactorings as suggested by Steve Dower.

- Removed unnecessary if check on std_abbr

    Discovered this because of a missing line in branch coverage.

1 files changed, 46 insertions, 0 deletions

diff --git a/configure b/configure
index 64bcde6..56d66d0 100755
--- a/configure
+++ b/configure
@@ -658,6 +658,7 @@ LIBFFI_INCLUDEDIR
 PKG_CONFIG_LIBDIR
 PKG_CONFIG_PATH
 PKG_CONFIG
+TZPATH
 SHLIBS
 CFLAGSFORSHARED
 LINKFORSHARED
@@ -819,6 +820,7 @@ with_assertions
 enable_optimizations
 with_lto
 with_hash_algorithm
+with_tzpath
 with_address_sanitizer
 with_memory_sanitizer
 with_undefined_behavior_sanitizer
@@ -1525,6 +1527,9 @@ Optional Packages:
   --with-hash-algorithm=[fnv|siphash24]
                           select hash algorithm for use in Python/pyhash.c
                           (default is SipHash24)
+  --with-tzpath=<list of absolute paths separated by pathsep>
+                           Select the default time zone search path for zoneinfo.TZPATH
+
   --with-address-sanitizer
                           enable AddressSanitizer memory error detector,
                           'asan' (default is no)
@@ -10154,6 +10159,47 @@ $as_echo "default" >&6; }
 fi
 
 
+validate_tzpath() {
+    # Checks that each element of hte path is an absolute path
+    if test -z "$1"; then
+        # Empty string is allowed: it indicates no system TZPATH
+        return 0
+    fi
+
+    # Bad paths are those that don't start with /
+        if ( echo $1 | grep -qE '(^|:)([^/]|$)' ); then
+        as_fn_error $? "--with-tzpath must contain only absolute paths, not $1" "$LINENO" 5
+        return 1;
+    fi
+}
+
+TZPATH="/usr/share/zoneinfo:/usr/lib/zoneinfo:/usr/share/lib/zoneinfo:/etc/zoneinfo"
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for --with-tzpath" >&5
+$as_echo_n "checking for --with-tzpath... " >&6; }
+
+# Check whether --with-tzpath was given.
+if test "${with_tzpath+set}" = set; then :
+  withval=$with_tzpath;
+case "$withval" in
+    yes)
+        as_fn_error $? "--with-tzpath requires a value" "$LINENO" 5
+        ;;
+    *)
+        validate_tzpath "$withval"
+        TZPATH="$withval"
+        { $as_echo "$as_me:${as_lineno-$LINENO}: result: \"$withval\"" >&5
+$as_echo "\"$withval\"" >&6; }
+        ;;
+esac
+
+else
+  validate_tzpath "$TZPATH"
+ { $as_echo "$as_me:${as_lineno-$LINENO}: result: \"$TZPATH\"" >&5
+$as_echo "\"$TZPATH\"" >&6; }
+fi
+
+
+
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for --with-address-sanitizer" >&5
 $as_echo_n "checking for --with-address-sanitizer... " >&6; }